Manufacture of trusses

ABSTRACT

A plurality of wooden roof trusses for constructing a roof includes first and second wooden roof trusses. Each of the first and second wooden roof trusses includes a bottom chord and at least one upper chord obliquely disposed relative to the bottom chord. A first web is provided to the first wooden roof truss and a second web is provided to the second wooden roof truss. Each of the first and second webs has a tapered web end shape set without regard to a shape of a first and second joint, respectively, into which said tapered web end shapes of the first and second webs fit. The first and second webs are substantially identical in length and web end shape. The first and second webs are located at different positions in their respective first and second wooden roof trusses.

This invention relates to the manufacture of wooden roof trusses, of thekind including a bottom chord and at least one upper chord obliquelydisposed in relation to the bottom chord, webs being connected betweenthese chords.

In the manufacture of a set of such roof trusses it is customary tocalculate, with the aid of a computer program, the composition of eachtruss according to span and loading, in the course of which the lengthand end cut geometry of each web, and its position in a truss, aredetermined. In a given set of trusses for a roofing job, there will be agreat number of different webs which must be cut and correctly locatedduring assembly.

We have found that it is possible to produce structurally satisfactorytrusses in the varying sizes and types required in roofing construction,in which the webs are selected from a set of standard stock web lengths,with the panel points being determined by the successive selection ofweb lengths from stock lengths, and in which the ends of the webs areprovided with a standard shape, set without regard to the geometry ofthe particular joints at which the ends are actually to be used.

In this way webs may be manufactured in advance of use and drawn fromstock according to the specifications of a given job, with resultantcost savings.

In the preferred form of such webs, the ends are formed as semi-circleswith a diameter substantially corresponding to the width of the web andtheir centres on the axis of the web.

U.S. Pat. No. 3,867,803 discloses a parallel chord joist truss in whichthe webs have such standardised end shapes. Unlike parallel chordtrusses, however, the production of gable trusses and other roof trusseshaving oblique chords by the use of known procedures requires theproduction of webs of many specific lengths for a given job.

In its second aspect, the present invention provides methods of choosinga satisfactory web combination using the stock web lengths available, toachieve the desired structural performance. Whereas in the conventionalapproach, the panel points of the truss have been determined by thegeometry of the chords (for example, where, in a so-called Fink truss,the panel lengths of the top chords are equalised, as are the panellengths of the bottom chord, thus specifying the position of the panelpoints), in accordance with the present invention the actual panelpoints are determined by choosing webs from the stock lengths accordingto a predetermined scheme. The preferred schemes described herein relatethe actual panel points defined by web selection to the panel pointsdefined by panel length equalisation, for example by choosing a weblength which will locate the actual panel point most closely on apredetermined side of the relevant notional panel point or by choosingwebs which will contact the chords within provisionally determined panelpoint zones on the chords of the truss, the panel point zones beingchosen on the basis of structural considerations.

In one such approach the invention provides a method of manufacturingwooden roof trusses of the kind having a bottom chord and at least oneupper chord obliquely disposed relative to the bottom chord, the upperand bottom chords being connected by webs by means of nail-platedjoints, characterised in that at least some of the webs are selectedfrom a set of standard stock web lengths, and in that the ends of thosewebs are provided with a standard shape, set without regard to thegeometry of the joints at which the ends are to be used.

Preferably the stock of webs comprises a set of web lengths whichincrease by equal increments between minimum and maximum lengths.

Preferably also the panel points of the truss are determined by thesuccessive selection of web lengths from said stock.

In a particularly preferred form of the methods of the invention, themethod includes the steps of

-   -   a) determining notional panel points on the chords said panel        points being joined by notional web lines    -   b) choosing a starting point on a chord (“the starting chord”)    -   c) choosing successive webs from the stock of standard lengths        to form two alternating sets of webs such that        -   (i) in the case of one set of alternate webs, each web is            that for which the stock length is the longest not greater            than the distance from the joint of the web with the            starting chord to the notional panel point for that web on            the opposite chord and        -   (ii) in the case of the other set of alternate webs, each            web is that for which the stock length is the shortest which            is at least the distance from the connection of said web            with the opposite chord to the intersection with the            starting chord of a line passing through said joint and            parallel to the notional line of the web.

Preferably in such a method where the length thus determined of a web ofsaid other set of alternate webs is greater than the said distance fromthe connection of said web with said opposite chord to the intersectionwith the starting chord of said line, the joint of the second web withthe starting chord is located on the side of said intersection remotefrom the starting point.

Preferably also the starting point is the apex of the truss, and thenotional panel points of an upper chord are determined by dividing thechord into panels, preferably equal panels, and the notional panelpoints of the bottom chord are at the intersection with the bottom chordof lines, preferably normal to the upper chord, intersecting the upperchord at the notional panel points thereof.

In another approach to the criteria for web selection, target panelpoint zones are established on structural principles, and alternativemethods used to determine an efficient web layout within the constraintsof such zones. Such a method may include the steps of

-   -   a) determining the maximum allowable panel lengths for each        chord of the truss    -   b) determining the minimum number of overlapping maximum panel        lengths in each chord, the regions of overlap thereof being        referred to herein as panel point zones    -   c) selecting webs from the stock range on the basis of chosen        criteria including the requirement that the chosen web will        connect with the chord within a target panel point zone        previously determined for the next web-to-chord joint.

Each of these alternative methods is characterised by a stepwiseprocedure reiterated where necessary, in which, starting at a chosenpoint on the truss, preferably either

-   -   (a) starting at the apex (or other point where the angle of the        chord changes) and working toward the heels of the truss, or    -   (b) starting at the heels and working toward the apex, or    -   (c) starting with the provision of a king post and starting        other web selection from the foot of the king post and working        toward the heels        webs are selected from the stock range on the basis of chosen        criteria including the requirement that the chosen web will        connect with the chord within a target panel point zone        previously determined for the next web-to-chord joint.

One of these alternative methods begins by establishing all possiblecombinations of webs satisfying the requirement that they begin and endin a panel point zone. A choice is then made between these combinationson the basis of a pre-determined criterion or set of criteria. Suitablecriteria for this purpose include

-   -   (a) the sum of the individual departures of the panel points        from the location of corresponding panel points in a standard        solution, and    -   (b) timber usage.

Other criteria may be adopted.

In the second of the alternative methods, webs are chosen on the basisof a parameter extreme, for example,

-   -   (a) the web which hits the target panel point zone at a position        within that zone closest to the starting point (eg. the apex or        centre of the truss).    -   (b) the shortest stock length which will reach the target panel        point zone,    -   (c) the longest stock length which will reach the target panel        point zone.

Other possible bases for web choice include choosing the web for whichthe included angle between the web and the chord is closest to apreferred angle for the panel point in question.

As a matter of convenience, the invention will be described primarily inits application to symmetrical trusses having a pair of upper chordmeeting at a centrally located apex, but it is to be borne in mind thatthe invention may be applied, with appropriate modifications, to othertypes of trusses. Also as a matter of convenience, the trusses will bedealt with in the description of assembly methods in terms of singledimension line drawings, thereby avoiding the need to be concerned withweb width and end shape, and with the choice of measurement conventions,for example the choice between the use of internal or externaltriangles. As is well known, various conventions are used in definingtruss dimensions, particularly chord length. Providing the structuralimplications of the convention employed are taken into account, however,the choice of convention is of no relevance to the present invention.

In the drawings,

FIG. 1 illustrates a web for use in the practice of the invention.

FIGS. 2 to 4 show three common forms of truss, respectively having two,four and six webs on each side, configured conventionally with equalpanels in the upper chords and equal panels in the lower chords;

FIGS. 5 and 6 illustrate web to chord joints employing webs of the kindillustrated in FIG. 1;

FIGS. 7 to 9 illustrate web to chord joints employing alternative webend shapes;

FIGS. 10 to 14 schematically illustrate a method of web selectionaccording to one embodiment of the invention;

FIGS. 15 to 19 schematically illustrate a method of web selectionaccording to another embodiment of the invention; and

FIG. 20 schematically illustrates a method of web selection according toanother embodiment of the invention.

Illustrated in FIG 1 is a web 50 made for the purposes of the invention,provided with semi-circular ends 49 the radius of which is one half ofthe web width. While end shapes other than a semicircle may be used, asdescribed below, this is the preferred form.

In accordance with the invention, either at the mill or in the trussfactory, webs are cut with such ends, in a standard range of lengths.The optimum length range and the optimum increment by which web lengthincreases from one standard length to the next will to some extentdepend on the range of truss types and sizes being manufacture, but as aguide, in the manufacture of roof trusses for housing in SydneyAustralia, lengths in 150 mm increments between 150 and 3600 mm havebeen found suitable. The increments by which the length of the websincrease need not be equal, and benefit may be found in someapplications in adopting a scheme whereby the length increments as afunction of length, for example geometrically or logarithmically, orindeed random predetermined lengths may be employed.

FIG. 5 illustrates a typical joint between a single web 50 and a chord51, effected by means of a conventional nail plate 52, while FIG. 6shows a joint involving two such webs. The use of nail plates in thefabrication of wooden trusses is well known, and conventional nailplates may be used in conjunction with the present invention.

FIG. 7 shows a joint in which the web ends instead of beingsemi-circular are formed with a radiused end and a tapering section 53on one side. FIG. 8 shows a joint in which the web ends have a taper 53on both sides and a radiused end of consequently smaller radius. Anextreme example is shown in FIG. 9, which shows a joint in which the webends are simply cut to form oblique faces 54.

Alternative end formations may be employed, for example the standard endmay consist of a series of cuts at successive angles, or a combinationof such cuts with radiused portions.

What all such shapes including the preferred semicircular shape have incommon is the provision of some form of taper, which reduces the gapwhich will be produced between the ends of the webs and the chord, andbetween abutting web ends. Of these tapering shapes, the semicircularshape is preferred for the reason that the gap between the chord and apair of web ends, or between a single web and a chord, is constant forvarying web angles.

The web selection methods of the invention for such truss types will nowbe described. As a matter of convenience, and because it may bestintroduce the reader to the concepts involved, the alternative methodsof web choice will be described first, followed by the most preferredmethod.

The first methods to be described make use of the concept of panel pointzones which are chosen by first determining in accordance with criteriaadopted for the purpose, the maximum allowable panel lengths for thechords, for a given choice of factors which may include chord sectionand grade, web configuration, chord length and truss loading.

The maximum allowable panel lengths may be determined from firstprinciples, based on the allowable loading of the timber sections inquestion. The maximum allowable panel lengths determined in this way maydiffer for the different panels of each chord.

Other methods may be employed for the determination of the allowablepanel lengths. For example, the lengths may be determined by examiningthe panel lengths in a conventionally designed truss for the maximumspan allowed for that truss type for the timber section and quality tobe employed. In such a conventionally designed truss, the equal panellengths will not be equally stressed, so deriving the maximum allowablepanel length in this way will give a conservative figure.

In the preferred practice of the invention, panel point zones, or atleast the panel point zones after the first zone in the sequence of webplacement, are determined initially as provisional zones, by providingthe minimum number of substantially equally overlapping maximumallowable panel lengths in each chord. The provisional panel point zonesare the regions of overlap of these panel lengths. The panel point zonesafter the first from the starting point are revised upon thedetermination of the location of the preceding panel point on the chordin question, again by reference to the maximum allowable panel length orby calculation. The webs are then chosen, either by the method ofestablishing all possible combinations and then choosing the combinationwhich best satisfies the chosen criteria, or by choosing successive websaccording to one of the other methods described above.

In the case where web lengths are determined progressively, it may occurthat there is no available web length between the last located panelpoint and any point in the next panel point zone. In such a case theprevious web is replaced by an alternative, preferably the nextincremental web length away from the starting extreme, and the next webselection reiterated. If again no web length is suitable, the previousweb is again replaced, by the next length again away from the extreme,and so on. Where this procedure does not produce a result, then the webpreceding this immediately preceding web is substituted in the same way,until a fit is found. Where no fit can be found in this way, the numberof webs is increased and the procedure repeated until a fit is found.

The application of this approach to the design of a symmetrical trusswith four webs per side will now be described.

The truss design will normally take place within the context of theparameters of truss sizes, chord materials and loadings standardised fornormal production for the plant. A typical set of such parameters may beas follows:

-   -   Span range: To 10000 mm    -   Pitch range: 18 to 26 degrees    -   Preferred top chord material: F5 JD5 90×35 mm kiln dried pine    -   Preferred bottom chord material: F5 JD5 90×35 mm kiln dried pine    -   Roof Loadings: Terra Cotta tiles    -   Ceiling Loadings: Plasterboard 13 mm        Design wind speed: 41 m/sec    -   Top Chord bracing: Tile battens@300 mm ctrs    -   Bottom Chord bracing: Bracing at 1800 mm in ctrs

For these parameters a suitable top chord maximum allowable panel lengthmay be for the truss in question 2100 mm, and for bottom chords 2700 mm.

The span and pitch of the truss and the material section determine theinternal or external triangle of the truss and the dimensions of thechords. Once this is determined, the next step is to locate the panelpoint zones, by locating substantially equally overlapping units of themaximum allowable panel lengths l₁ and l₂ along the respective chordsfrom the apex and from the heels as shown in FIG. 10.

In the present example two such zones 14 and 15 are determined on eachof the top chords 11 and 12, while the bottom chord 13 has two pairs ofzones 16 and 17.

The preferred starting point for the web selection is the apex of thetruss, since this is a fixed location. While it is possible to work fromthe heel towards the apex, this has the difficulty that the end point ofthe process is inflexible, unless one is prepared to tolerate a truss inwhich the central webs do not meet the upper chords at the apex.

In the following description, the choice of webs will be discussed inrelation only to the left-hand side of the truss as viewed in FIG. 10,since the truss is symmetrical and the same results will be obtained onthe other side.

Where the truss design is to be solved by determining all possible webcombinations which satisfy the available stock lengths and the panelpoint zones, the possible choices of first web 18 (FIG. 11) aredetermined, shown in this example as 18 a, 18 b and 18 c.

For each of these solutions for the first web 18, the family of webs 19meeting the target panel point zone 14 is then determined. In theexample shown in FIG. 12, for the case of web 18 a, the possible familyis 19 aa, 19 ab, 19 ac (FIG. 12). It is to be observed that a web may becapable of meeting a panel point zone in two places. In such a case,both possibilities will preferably be used.

For each of the possible webs 18 a, 18 b and 18 c (FIG. 11), the targetpanel point zone 17 is re-calculated by measuring out the relevantmaximum allowable panel length from each of the panel points of thesepossible webs, producing a family of overlapping zones 17 a, 17 b, 17 c.Similarly for each member of the family of possible webs 19, such as 19aa, 19 ab, 19 ac (FIG. 12), a family of target panel point zones 15 a,15 b, 15 c, . . . is calculated.

This procedure is repeated along the truss until all web families havebeen determined. At this point a large family of trusses will have beengenerated, each of which could be manufactured from the available stock.

Preferably, each of these truss designs is examined to identify thosewhich incorporate web geometry which is undesirable, for example, wherethe minimum included angle between a web and the chord to which it isattached is not reached for unopposed joints of webs which are to actin, or may go into, compression. In such cases the truss may be deleted,or the joint modified to provide opposition for the web, for example byadding a block attached to the chord or by adding a further web.

Once such exceptions have been taken care of, a choice is made betweenthe remaining truss solutions, on the basis of a predetermined criterionor set of criteria. Preferably, this is done by comparing each of thetrusses with a truss which would have been manufactured using prior arttechniques. The preferred method of comparison is to take one truss at atime, and measure the distance between each panel point of the truss andthe corresponding panel point of the prior art truss. Each of thesedistances is then totalled for each truss. The chosen truss will be theone which has the smallest total, indicating close correspondence withthe prior art solution.

As indicated above, some other basis of choice may be made, for examplebased on the quantity of timber used by each truss solution.

An example will now be described of the way in which the truss may bedetermined by the sequential selection of webs by the adoption of webswhich satisfy a parameter extreme, in this example, the web which landsat a point in the target panel point zone which is closest to thestarting point of web selection.

The first web 18 (FIG. 13) is chosen as that web from the stock lengthsof web which will extend from the apex and contact the bottom chordwithin the zone 16 at the point closest to the centre of the truss. Withthe selection of this web, the panel point zone 17 can now be determinedby measuring out the relevant maximum allowable panel length from thepanel pont of the web 17 towards the heel.

The next web to be chosen, web 19, is that having the stock length whichwill extend from a joint at the lower chord adjacent the web 18, andstrike the upper chord 11 within the provisional panel point zone 14,closest to the apex of the truss. The selection of web 19 then allowsthe determination of panel point zone 15. Similarly, the next web 20 ischosen as the stock length which will extend from the joint with web 19on the upper chord 11 and contact the lower chord 13 within the panelpoint zone 17 and closest to the centre of the truss.

Finally the web 21 is chosen as the stock length which will extend fromthe joint with web 20 on the lower chord 13 and contact the upper chord11 within the provisional panel point zone 15, closest to the apex.

Before the web layout thus arrived at can be considered complete, theangle of contact between compression webs (or tension webs which may gointo compression, for example under wind uplift) and the chord at anunopposed joint (i.e. a joint comprising a chord and only one web),should be checked to ensure that it is not so small as to beunacceptable for the nail plate fixing employed. It will be foundconvenient to adopt a minimum angle based on testing of such joints, andto reject designs which produce an angle at an unopposed joint which isless than this minimum angle. With the parameters employed in thepresent examples, such a minimum angle may be found to be in the regionof 10 to 30 degrees.

Where the web angle is found to be less than the minimum, it will benecessary either to revise the preceding web choice, or to use otherexpedients such as the use of a block attached to the chord to provideopposition for the web, or add a further web to provide this opposition.

FIG. 14 illustrates a case in which web length selection must reiteratedto achieve the truss design. Here it is shown that after the initialchoice of the web 18, in seeking the correct length for the next web itis found that while the web length 119 is too short to reach the zone14, the next longest web 219 is too long. In this case the web 18 isreplaced by the next greater stock length landing in the target panelpoint zone 16, i.e. the next stock length web landing away from the apexof the truss. This will generate a new starting point for the next web,whereupon it may be found that the web 119 or a web of another stocklength reaches the provisional zone 14.

Should this reiteration of the procedure not produce a workable choicefor the next web, the first web length is again incremented, and a fitfor the second web sought afresh.

It will be understood that this procedure will be used to overcome theabsence of a suitable web length at any of the successive web locationsalong the truss. In an extreme case it may be necessary to carry thereiteration of length determination back for more than one web in thesequence.

In the case where the first web choices are exhausted without finding asuitable truss, or without finding an available web length for a givenweb, then the configuration of the truss must be revised, increasing thenumber of webs.

In most cases it will be found that more than one set of webs can befound for a given truss, if the designer experiments with differentstarting web lengths or substitutes intermediate webs. In such cases,even where the method of determining webs successively is employed, themanufacturer may prefer to generate a family of possible web choices fora given truss, and choose from among these the pattern of webs whichbest suits the application, for example by providing room forair-conditioning ducts, or for personnel access in the roof. Indeed, thedesigner conscious of such additional design parameters will modify hischoices of web length at the appropriate part of the truss to take theseinto account, choosing, for example, a longer web at a particular pointthan would otherwise be suggested by the simplest form of the methoddescribed above.

In conjunction with the approach to truss design thus described, afurther modification to normal practice can be of advantage. In thismodified approach, joints comprising more than one web end are modifiedso that the web ends are spaced along the chord (or, at an apex, theirrespective chords). Preferably a standard spacing is adopted which iscompatible with the structural requirements of the truss, but thespacing may be varied within a given truss, and not all joints may bedesigned in this way. A typical spacing of the web ends in roof trussesmay be 200 mm.

The use of open joints of this kind provides several advantages in themethod of the present invention. The panel point zone may be extended,and consequently the number of web lengths in the stock family may bereduced, by increasing the length increment between successive stocklengths. This approach will also enable some trusses to be constructedwith less webs than otherwise. For example, a truss which had to beconstructed with six webs per side because a web length/zone fit couldnot be found for the case of four webs per side may, with spaced joints,have four webs per side.

The methods thus described may be implemented by computer or conductedmanually. Computer implementation will be of particular benefit where itis desired to generate a family of web solutions.

FIGS. 15 to 19 illustrate another approach to the web selection process,foreshadowed above and having the advantage of starting with a clearlydefined chord geometry. In this method, as shown in FIG. 15 there isfirst provided a king post 22 cut to the correct length if necessary,descending vertically from the apex of the web. By fixing such a web inposition before fixing the remaining webs the chords are now fixed inposition with an accurately defined apex height, whereas in the methodspreviously described the truss triangle was not fixed until webinstallation was substantially complete.

The subsequent webs may now be selected according to the method andcriteria described above, leading to the development of trusses as shownin FIGS. 16 to 19

A preferred method of web selection, which is particularly well adaptedto embodiment in computer software, will now be described.

In the truss illustrated in FIG. 20, each of the upper chords is, as isconventional, divided into equal panel lengths to define upper chordnotional panel points 23 and 24. Parallel lines 25 and 26 are then drawnintersecting the upper chords at each of the notional panels points todefine at their intersections with the bottom chord, notional panelpoints 27 and 28. The angle between the relevant upper chord and thelines 25 and 26, which may be regarded as notional web lines, issuitably 90 degrees, but other angles may be used and chosen onstructural principles or by experiment In the example illustrated, anangle of 90 degrees will be used.

Lines 29 and 30 are shown as the notional web lines joining the apex andpanel point 27, and panel points 23 and 28.

The object of the web selection method now employed is to select webswhich determine panel points on the bottom chord having a closecorrespondence with the notional panel points. This is done by starting(preferably) at the apex of the truss, and choosing for each side of thetruss the greatest web length 30 which will produce a joint at or on thenear side of the notional panel point 27. In other words, the web lengthchosen is the longest in the stock of lengths which is not greater thanthe distance between the apex and the notional panel point 27.

From the actual panel point 27 a thus established on the lower chord 13,a line 25 a is drawn parallel to the line 25 intersecting the upperchord 11. The next web 31 is chosen as the web with the shortest stocklength which is not less than the distance between the panel point 27 aand the intersection of the line 25 a with the upper chord 11.

Except in the rare case that there is a stock length equal to thisdistance, the web 31 can form a joint with the upper chord in either oftwo locations, one on each side of the line 25 a. Preferably the web ispositioned with its joint on the upper chord on the side of the line 25a remote from the apex, since in this way the resultant web layout willmost closely approximate the notional layout. The location of theresulting panel point 25 b relative to the notional panel point 23 willdepend on the length of the web 31 and the other relevant parameters ofthe web, but it will be found that for a practical choice of web lengthincrements as discussed above, the point 25 b will be quite close to thenotional point 23.

This process is repeated, with the web 32 being chosen for the greatestlength from the stock lengths which will produce a joint at or on thenear side of the notional point 28, and the web 33 as the shortest stocklength which is not less than the distance between the panel point 28 aand the intersection of the line 26 a with the upper chord 11. As in thecase of the web 31, the web 33 is positioned with its upper panel pointon the side of the line 26 a remote from the apex (i.e. closest to thenotional panel joint 24). The effect of this methodology will be seen tobe to group the actual panel points as closely as possible to thenotional points, with a simple, unambiguous basis for web length choicein each case. It may also be observed that by choosing the angle betweenthe upper chord 11 and the notional web lines 26 as 90 degrees, thelikelihood that an unopposed web to chord joint such as that of the web33, will be made at an angle less than the minimum web angle discussedabove, is very small, since such a large departure from parallelismbetween the actual web line and the line 26 a is unlikely.

This last described method may be varied, if desired, for example byreversing the sides of the lines 25 and 26 and/or 25 a and 26 a on whichthe respective web ends fall.

As in the methods previously described, the web layout thus arrived atwill be checked for compliance with the predetermined minimum web angle,and if this requirement is not satisfied, then either a block will beadded to the chord to oppose the web at the offending joint, or afurther web added for this purpose. Alternatively, the designer maychoose to repeat the web selection process for a truss with anadditional web on each side.

Preferably, the truss will also be checked to ensure that the panelpoints established by this process of web selection satisfy thestructural requirements of the truss application. This can be done bychecking the truss by first principles, or by determining that the panelpoints land within the panel point zones determined as described above.If this is not the case, then one or more webs should be added to thedesign and the web selection process repeated.

While this last methodology has been described in terms of working fromthe apex (or other point of chord angle change) it is to be appreciatedthat this method also may be practiced by starting elsewhere, forexample at the notional panel point closest to the heel of the truss,with choices of the alternative actual upper panel point locations beingmade, as above, preferably in a way which results in a web layoutapproximating the notional layout. Other starting points may be chosen,for example on the notional panel points on either chord, or any pointwithin any panel point zone, or at a panel point determined by prior artmethods.

The invention may be applied to trusses other than the simpleend-supported gable trusses discussed so far. Examples of other trussesto which the invention may be applied are cantilevered trusses wherediffering panel lengths may apply in the cantilevered portion of thetruss, or trusses with additional supports, truncated trusses, mono andcut-off mono trusses, cut-off gable trusses and valley trusses. In allthese and other cases not listed here the same basic proceduresdescribed above may be practised.

It will be understood that there may be instances where, because of thetype of truss, or the need to include an extreme web to truss angle, oneor more conventionally cut webs of non-standard length may have to beincorporated in a particular truss. The invention extends to such mixedtrusses, where the time and labour saving offered by the use of theinvention will still largely be obtained.

1-27. (canceled)
 28. A stock of webs for constructing an oblique rooftruss, comprising a plurality of structural wooden webs having asubstantially identical tapered end shape and being of discrete lengthsat increments of between a minimum web length and a maximum web length.29. The stock of webs for constructing an oblique roof truss accordingto claim 28, wherein said substantially identical tapered end shape issubstantially semicircular.
 30. The stock of webs for constructing anoblique roof truss according to claim 28, wherein said discrete lengthsare at substantially equal increments.
 31. The stock of webs forconstructing an oblique roof truss according to claim 30, wherein saidsubstantially equal increments are approximately 150 mm.
 32. The stockof webs for constructing an oblique roof truss according to claim 28,wherein said substantially identical tapered end shape is formed as aseries of cuts at successive angles.
 33. The stock of webs forconstructing an oblique roof truss according to claim 32, wherein saidseries of cuts at successive angles forms a convex, substantiallyarcuate end shape.
 34. The stock of webs for constructing an obliqueroof truss according to claim 33, wherein said discrete lengths are atsubstantially equal increments.
 35. The stock of webs for constructingan oblique roof truss according to claim 28, wherein said substantiallyequal increments are 150 mm.